1. Field of the Invention
The invention relates to a system and a method for providing hearing assistance to at least one user, wherein audio signals from an audio signal source, such as a microphone for capturing a speaker's voice, are transmitted via a wireless link to a receiver unit, such as an audio receiver for a hearing aid, from where the audio signals are supplied to a means for stimulating the hearing of the user, such as a hearing aid speaker.
2. Description of Related Art
Usually in such systems the wireless audio link is an FM (frequency modulation) radio link. According to a typical application of such wireless audio systems, the receiver unit is connected to or integrated into a hearing instrument, such as a hearing aid, with the transmitted audio signals being mixed with audio signals captured by the microphone of the hearing instrument prior to being reproduced by the output transducer of the hearing instrument. The benefit of such systems is that the microphone of the hearing instrument can be supplemented or replaced by a remote microphone which produces audio signals which are transmitted wirelessly to the FM receiver, and thus, to the hearing instrument. In particular, FM systems have been standard equipment for children with hearing loss in educational settings for many years. Their merit lies in the fact that a microphone placed a few inches from the mouth of a person speaking receives speech at a much higher level than one placed several feet away. This increase in speech level corresponds to an increase in signal-to-noise ratio (SNR) due to the direct wireless connection to the listener's amplification system. The resulting improvements of signal level and SNR in the listener's ear are recognized as the primary benefits of FM radio systems, as hearing-impaired individuals are at a significant disadvantage when processing signals with a poor acoustical SNR.
A typical application of such wireless audio systems is at school, wherein the teacher uses a wireless microphone for transmitting the captured audio signals via the transmission unit to receiver units worn by the students. Since the receiver units and the respective hearing aids are usually owned by the students, the receiver units may be of different types within a class.
Another typical application of wireless audio systems is the case in which the transmission unit is designed as an assistive listening device. In this case, the transmission unit may include a wireless microphone for capturing ambient sound, in particular from a speaker close to the user, and/or a gateway to an external audio device, such as a mobile phone; here, the transmission unit usually only serves to supply wireless audio signals to the receiver unit(s) worn by the user.
Examples of analog wireless FM systems particularly suited for school applications are described, for example, in European Patent Application EP 1 863 320 A1 and International Patent Application Publication WO 2008/138365 A1, which corresponds to U.S. Patent Application Publication 2011/0044481 A1. According to these systems, the wireless link does not only serve to transmit audio signals captured by the wireless microphone, but in addition also serve to transmit control data obtained from analyzing the audio signals in the transmission unit to the receiver unit(s), with such control data being used in the receiver unit to adjust, for example, the gain applied to the received audio signals according to the prevailing ambient noise and the issue of whether the speaker is presently speaking or not. For transmission of such control data, the range between 5 and 7 kHz of the transmitted bandwidth, i.e., a frequency band above the audio signal band, may be used.
In applications where the receiver unit is part of or connected to a hearing aid, transmission is usually carried out by using analog FM technology in the 200 MHz frequency band. In recent systems, the analogue FM transmission technology may be replaced by employing digital modulation techniques for audio signal transmission. An example of such digital system is available from the company Comfort Audio AB, 30105 Halmstad, Sweden under the designation “Digisystem”, (see the company website).
A specific example of an analog wireless FM system particularly suited for school applications is described in International Patent Application Publication WO 2008/074350 A1 which corresponds to U.S. Pat. No. 8,144,903 B2, wherein the system consists of a plurality of transmission units comprising a microphone and a plurality of analog FM receiver units and wherein only one of the transmission units has an analog audio signal transmitter, while each of the transmission units is provided with a digital transceiver in order to realize an assistive digital link for enabling communication between the transmission units. The assistive digital link also serves to transmit audio signals captured by a transmission unit not having the analog transmitter to the transmission unit having the analog transmitter from where the audio signals are transmitted via the analog FM link to the receiver units.
Digital audio signal transmission is also used in the field of mobile telephony, wherein it is known to provide a mobile telephone with the option to operate in different networks, for example GSM900 and GSM1800, including services like GPRS and EDGE, and UMTS, including services like HSDPA and HSUPA. However, at a time, always only one of these options is used, depending on the present network.
It is also known that special security relevant applications, such as navigation systems, flight and/or space communication systems and personal safety systems, may utilize redundant radio systems in order to improve robustness and to guarantee operation also in case of failure of one of the radio units. Naturally, always the same radio technology is used for the redundant link, and only one of the links is operated at the same time.
In radio broadcasting or TV broadcasting, it is known to transmit mixed analog and digital signals, see, for example, U.S. Pat. No. 6,418,300 B1, German Patent Application DE 37 18 906 A1, German Patent Application DE 197 17 169 A1 and International Patent Application WO 00/21228 A1 that corresponds to U.S. Pat. No. 6,570,943 B2.